The growth of portable, personal electronics devices such as cellphones, PDAs, and similar devices, has spurred development of miniaturized cameras and light-sensing components that can be incorporated into these devices. The continuing demand for smaller and more powerful imaging apparatus, coupled with the requirement for low cost, presents a considerable challenge to optical and mechanical design. Low-cost lens assemblies, typically including a number of plastic lens elements, are being used increasingly for these applications. As lenses become smaller, however, there are a number of practical considerations that are of comparatively little concern for design of larger optical systems.
Although very small plastic lenses can be fabricated inexpensively at high volumes, the handling, alignment, and mounting of these tiny optical components into a lens assembly using multiple components poses significant problems. A number of conventional approaches have been applied to the problem of plastic lens mounting, alignment and centration of lenses, including the use of features formed within a lens barrel or other supporting structure. Kinematic component mounting techniques, such as those disclosed in U.S. Pat. No. 6,400,516 entitled “Kinematic Optical Mounting” to Spinali take advantage of ease of fabrication to provide additional structures outside the optical area of the lens, such as radial tabs or other protrusions. Various types of fasteners, clamps, springs, fittings, or adhesives have been employed to mount these miniaturized optical components. However, as is exemplified in the Spinali '516 disclosure, some approaches may prove to be too complex for low-cost, miniaturized optical systems. Even adhesives require some surface area for their application, which can reduce the effective diameter of a barrel structure, for example.
It is known to provide tabs or other peripheral mounting and handling structures on optical components. However, many applications using tab structures are inappropriate for small scale lens assemblies, particularly for plastic lens elements. For example, U.S. Pat. No. 4,854,671 entitled “Mount for Optical Elements” to Hanke et al. discloses a lens assembly in which elastic ribs are applied to form tabs on the lens perifery, then are compressed to hold the lens in place. Notably, however, the elastic tabs are of a different material from the lens.
Other approaches to the lens mounting problem combine tabs or protrusions on the lens with features built into a lens mount, holder, or barrel. For example, commonly assigned U.S. Pat. No. 5,249,082 entitled “Exact Constraint Arrangement for and Methods of Mounting an Element Such as a Lens” to Newman discloses a lens holder that provides a three-pin engagement for radially extended tabs on a lens element. Similarly, U.S. Pat. No. 5,642,235 entitled “Lens Supporting Device” to Ichikawa show the use of various tab mating features in a lens supporting sleeve.
Still other approaches for lens mounting take advantage of the conformability of resilient plastic materials used as lens barrels or mounting rings. For example, U.S. Pat. No. 6,714,366 entitled “Optical Component Mounting Apparatus” to Wisecarver et al. discloses the use of a flexible sidewall for mounting a lens within a lens mounting sleeve.
Referring to FIG. 1, another conventional solution in a lens mount assembly 10 uses a retaining ring 12 for holding a lens element 14 in place within a barrel 16. Adhesive is then used to hold retaining ring 12 in place once it is properly positioned. Retaining structures such as retaining ring 12 are advantaged for temporarily positioning lens element 14 until adhesive has fully cured. Other methods may not use any type of retaining structure, gluing lens element 14 directly to barrel 16.
Such conventional solutions for plastic lens mounting typically place an undesirable constraint on lens size. For many applications, such as when used in the portable electronic devices noted earlier, lenses must provide maximum light throughput with a clear aperture as large as possible. Constraining the lens area within a surrounding structure such as shown in FIG. 1 and as described in the '082 Newman and '235 Ichikawa disclosures, can effectively reduce the effective or clear aperture of the lens that can be used and limits the light throughput. Certainly, increasing the size of a lens mounting or barrel OD is a possible solution; however, in the miniaturized applications of interest, increasing the dimensions of mounting components is not an available option.
Thus, it can be seen that there is a need for a lens mounting arrangement that maximizes the clear aperture of the lens when using a barrel- or sleeve-mounted lens element, that minimizes the outer diameter (OD) of the lens barrel or other mounting structure, and that can be provided at relatively low cost.